Synthesis and characterization of bio-based epoxy thermosets using rosin-based epoxy monomer

Acrylicpimaric acid-based epoxy (APA-based epoxy) and tung oil maleic anhydride (TMA), as a curing agent, were synthesized and used to prepare fully bio-based cured epoxies. The chemical structure was characterized by FTIR and 1 H NMR spectroscopy techniques. The effects of using APA-based epoxy to replace DER332 epoxy were investigated. The curing behavior, dynamic mechanical properties, mechanical properties, thermal stability and fracture surface were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), a universal testing machine, thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The activation energy ( E a ) of the curing process of the APA-based epoxy with TMA was 69.45 kJ/mol, which was almost the same as the E a of the curing of DER332 process with TMA. Because of the rigidity of the hydrogen phenanthrene ring structure in the APA-based epoxy was higher than that of bisphenol A structure in DER332, the glass transition temperature ( T g ) of the cured APA-based epoxy was 21 °C higher than that of the cured DER332 epoxy. The tensile strength, Young’s modulus and the peak temperature of the weight loss rate ( T max ) of cured APA-based epoxy were higher than those of the cured DER332 epoxy. With a decrease in the APA-based epoxy content, the fracture surfaces of the cured APA-epoxy were much rougher. The cured APA-based epoxy exhibited higher storage modulus and Young’s modulus than the cured resins that were formed from flexible monomers. Therefore, the APA-based epoxy showed great potential to replace DER322 epoxy in preparing cured epoxies.